sanitize_user
Sanitize username stripping out unsafe characters.
If $strict is true, only alphanumeric characters plus these: _, space, ., -, *, and @ are returned.
Removes tags, octets, entities, and if strict is enabled, will remove all non-ASCII characters. After sanitizing, it passes the username, raw username (the username in the parameter), and the strict parameter as parameters for the sanitize_user filter.